A Radial Time Projection Chamber for $\hat{I}\pm$ detection in CLAS at JLab

Abstract

A new Radial Time Projection Chamber (RTPC) was developed at the Jefferson Laboratory to track low-energy nuclear recoils for the purpose of measuring exclusive nuclear reactions, such as coherent Deeply Virtual Compton Scattering and coherent meson production off ${}^4$He. In such processes, the ${}^4$He nucleus remains intact in the final state, however the CEBAF Large Acceptance Spectrometer (CLAS) cannot track the low energy $\hat{I}\pm$ particles. In 2009, we carried out measurements using the CLAS spectrometer supplemented by the RTPC positioned directly around a gaseous ${}^4$He target, allowing a detection threshold as low as 12$\sim$MeV for ${}^4$He. This article discusses the design, principle of operation, calibration methods and the performances of this RTPC.